The invention relates to a conveying apparatus for transporting and for measuring an object, the conveying apparatus comprising a sensor having a light transmitter that is arranged at a conveyor belt and that transmits first light beams in the direction of the conveyor belt, and having a light receiver that is arranged at the conveyor belt and that receives second light beams, and having an evaluation device for determining a dimension of the object by evaluating the received second light beams.
In the sector of the conveying and logistics industry, a continuous material flow is necessary at some points, with objects transported on a flat conveyor belt in a main conveying direction being detected at said material flow and optionally being measured with respect to their dimensions. This object is achieved as a rule by a volume measurement system for volume measurement by means of scanners, light barriers, light sensors or light grids as sensors.
Current volume measurement systems measure objects having a parallelepiped shape and/or having practically any desired shape on the conveyor belt. The volume measurement system contactiessly determines the real volume of the object as well as the length, width and height of the smallest encasing parallelepiped. In this respect at least one sensor is installed above the conveyor belt that scans the surface of the transported objects and provides the data to its interfaces for further processing.
The sensor transmits light beams in the direction of the conveyor belt and detects light beams reflected from the surface of the object when the light transmitter and the light receiver of the sensor are arranged on the same side of the conveyor belt or light beams not blocked by the object when the light transmitter and the light receiver of the sensor are arranged on oppositely disposed sides of the conveyor belt. In this context, the side of the conveyor belt on which the object lies is understood as the upper side of the conveyor belt and the oppositely disposed side of the conveyor belt is understood as the lower side of the conveyor belt.
The light beams of the sensor are not only reflected from the surface of the object, but also from the surface of the conveyor belt so that the conveyor belt effects interference noise in the measured signal of the sensor. This interference noise of the conveyor belt has the disadvantage that a measured signal of a very flat object on the conveyor belt is covered by the sensor in this so-called noise band. The height of the object can thereby not be detected or measured with sufficient accuracy.
For this reason, with the known volume measurement systems, a required detection line, the so-called trigger level, is set for the sensor so that only measured signals above the noise band of the sensor are taken into account for determining the height of the object. In other words, only objects having a minimum height can be detected and measured.
If an object has rising or falling body edges, the portions of the body, for example a width and/or a length, that are below the required detection line cannot be correctly detected An incorrect measured signal of the dimension of the object thereby results.
To avoid this disadvantage, a conveying apparatus for transporting and for measuring an object is known from EP 2 884 310 B1 in which two conveyor belts are arranged at one another with a marginal spacing. The sensor is arranged above and between the two conveyor belts so that a conveyed object can be measured at the point of the transition between the two conveyor belts.
It results from the arrangement of the conveying apparatus that a slip results between the movement of the conveyor belts and the movement of the object on the transition of the object from one conveyor belt to the other conveyor belt so that the measurement of the object is incorrect.